Physical Vapor Deposition (PVD) is a common process in micro-fabrication technologies. Referring to FIGS. 1A and 1B, a deposition system 100 includes a process chamber 110, a workpiece holder 120 that can hold a workpiece 130, a target 150, and a magnetron sputtering source 160. The target 150 can comprise a material to be sputtered by the magnetron-sputtering source 160 and deposited on the workpiece 130. The workpiece holder 120 and the workpiece 130 are typically stationary in the process chamber 110 during the deposition. The magnetron source is disposed in the vicinity of each target. The target is supported by a backing plate comprising inside a cooling system that can be a cooling water channels within the backing plate or a cooling liquid bath in which the the entire magnetron 160 and target 150 are immersed. During deposition, the magnetron-sputtering source 160 stays stationary or moves relative to the target 150. Only one material is deposited at a time in this configuration. The magnetron typically covers the entire target during deposition to maximize the usage of the target.
The workpiece can be a silicon wafer. The target material can include Au, Cu, Ta, Al, Ti, TiW, Ni, NiV etc. In a sputtering operation, a target comprising a desired sputtering material is first mounted in the process chamber 110. The process chamber 110 is pumped down to a reduced pressure. A layer of the sputtering material in the target is deposited on the workpiece 130 to form a deposition layer over the workpiece.
The micro-fabrication devices often require multilayer structures such as TiW/Au, Ti/TiN/Al, TaN/Ta/Cu to be deposited on the substrate of a silicon wafer without exposing to air between different layers. Even if air exposure is allowed between various film layers, the multi-layer deposition can be quite time consuming using the deposition system 100. The deposition of each layer requires a sequence of steps including the mounting of a target comprising the material for that layer, vacuum pump down, pressure adjustment and pressure stability, sputtering deposition to form the layer on the substrate of the workpiece 130, followed by the pressure increase and the target switching for the next deposition layer. A cleaning step may be added to avoid contamination between successive deposition layers. The same cycle is repeated for each of the deposition layers. In summary, the deposition of a multi-layer structure of the deposition system 100 requires a number of vacuum pump downs, pressure adjustment, target handling and mounting, and cleaning steps. The low system throughput limits the applications of the deposition system 100.
In another deposition system 200 as shown in FIGS. 2A and 2B, multiple pairs of targets 250 and 251 and magnetron sputtering sources 260 and 261 are enclosed in a single process chamber 210. Each of the magnetron sources 260 and 261 is disposed in the vicinity of its associated target 250 or 251. Each of the targets 250 and 251 is supported by a backing plate that can be cooled by a cooling system that can include channels within the backing plate for flowing a cooling fluid or a cooling liquid bath in which the targets 250 and 251 and the magnetron sputtering sources 260 and 261 can be immersed. During the deposition, workpieces 230 and 231 can be moved by a workpiece holder 220 to deposition areas and to receive the deposition of materials sputtered off targets 250, 251 without breaking the vacuum. The workpiece holder 220 and the workpieces 230 and 231 typically rotate around the center of the workpiece holder 220 in the process chamber 210. The magnetron sputtering source 260 and 261 can stay stationary or move relative to the targets 250 and 251 during deposition. Multiple materials can be deposited by moving the workpieces 260 and 261 under the different targets 250 and 251.
The deposition system 200 has a large footprint due to the housing of multiple workpieces and associated higher cost of manufacturing. The costs of target materials are also high because the targets need to be large enough to match the size of the workpieces. The disadvantages in cost and size limit the application of the deposition system 200.